Method for making dies

ABSTRACT

A DIE FOR CUTTING PAPERBOARD MATERIAL OR THE LIKE COMPRISES A PAIR OF DIE PLATES HAVING COACTING CUTTING ELEMENTS WHICH PARTIALLY OVERLAP IN THE PLANE OF THE MATERIAL TO BE CUT. IN MAKING THE DIE PLATES, TWO SEPARATE IMAGES REPRESENTING THE MALE AND FEMALE CUTTING ELEMENTS ARE SEPARATELY STEPPED AND REPEATED ONTO TWO SEPARATE SHEETS OF FILM TO PROVIDE MULTIPLE, LIKE IMAGES THEREON. ONE OF THE SEPARATE IMAGES IS STEPPED AND REPEATED THROUGH THE BASE OF THE RAW FILM ON WHICH THE MULTIPLE, LIKE IMAGES ARE IMPOSED WHEREBY EACH STEP AND REPEAT OPERATION ONTO THE TWO SEPARATE SHEETS OF FILM ARE EFFECTED IN THE SAME SEQUENTIAL ORDER LEADING TOWARD PRODUCTION OF A PAIR OF MATCHED, COACTING DIE PLATES.

July 13, 1971 KLEMM 3,592,651

METHOD FOR MAKING DIES Filed Nov. 12, 1968 2 Sheets-Sheet 1 FIG./

Z0 24 m; \\\w 25 2 35 if 36 juj 44 INVENTORS CARL JOHN KLEMM RICHARD AUGUST TIETZ BY ATTORNEY Jul 13, 1971 c. J. KLEMM ETAL 3,592,651

METHOD FOR MAKING DIES,

Filed Nov. 12, 1968 2 Sheets-Sheet 2 7a; R g #60 JAR, R R iq-54 R R J J R H R R S I /22 H R R 56, @5252, 56 flai 55 36X VW/i 56 INVENTORS CARL JOHN KLEMM RICHARD AUGUST TIETZ ATTORNEY United States Patent 3,592,651 METHOD FOR MAKING DIES Carl John Klemm, Appleton, Wis., and Richard August Tietz, Streamwood, Ill., assignors to American Can Company, New York, NY.

Filed Nov. 12, 1968, Ser. No. 774,716 Int. Cl. G034: 5/00 US. Cl. 96-36 3 Claims ABSTRACT OF THE DISCLOSURE A die for cutting paperboard material or the like comprises a pair of die plates having coacting cutting elements which partially overlap in the plane of the material to be cut. In making the die plates, two separate images representing the male and female cutting elements are separately stepped and repeated onto two separate sheets of film to provide multiple, like images thereon. One of the separate images is stepped and repeated through the base of the raw film on which the multiple, like images are imposed whereby each step and repeat operation onto the two separate sheets of film are effected in the same sequential order leading toward production of a pair of matched, coacting die plates.

BACKGROUND OF THE INVENTION This invention relates to a new and improved method of forming cutting, scoring and/or embossing dies, which are of particular value in the formation of paperboard carton blanks. Conventional dies for forming paperboard carton blanks consist of a male die made up of metal knives mounted in wooden furniture and a female die consisting of impressions cut in a paper member. It has been found that many costly and laborio s hand operations necessary for producing such conventional dies can be eliminated by the use of coacting, opposed dies formed from unitary metal plates having the working elements of the dies as an integral part thereof raised above the background areas of the die plates. Such dies may be formed economically by removing portions of a thin, metal plate by chemical means to form the background or depressed areas of the plate, leaving cutting and scoring lands standing above the background areas so formed.

An example of cutting, scoring and/ or embossing dies of the type to which this invention relates may be found in US. Pat. 3,142,233, issued July 28, 1964. As disclosed therein, the projecting lands of one die plate cooperate with the projecting lands on another die plate to effect a cutting or scoring of the material therebetween. The cooperating cutting lands overlap somewhat in the plane of the material but they do not touch one another during the cutting operation. The scoring is effected by a land on one die plate which forces the material between two spaced lands on the other die plate.

The die plates are used primarily for forming carton blanks from sheet material and thus the projecting lands are arranged in a pattern corresponding with the shape and formation of the carton blank to be cut and scored. It is necessary to obtain accurate registry between the two cooperating die plates so that the projecting lands on the matching die plates properly cooperate with one another to effect the desired cutting and scoring operation on the material.

In US. Pat. 3,341,329, issued Sept. 12, 1967, each of two photographic negatives bearing an image of one of the coacting cutting lands, including the overlapping por- 3,592,651 Patented July 13, 1971 tions of the cutting lands, is placed in contact with the surface of separate steel plates coated with photosensitive resist composition. The coating on each plate is then exposed to light from a source passing through the image on the negative, thereby to produce an image on the coating which becomes insoluble to the etching solution at the areas where it has been so exposed. After etching, the steel plates define two coacting, matched die plates, which carry the cutting and scoring elements as raised lands.

In order to obtain the desired cooperative matching of the lands on the two die plates, the orientation of the lands on the male and female die plates have to be reversed relative to one another. Accordingly, in producing matched die plates having multiple, like images, a film bearing a single image may be stepped in one sequential order for the male die plate and in another sequential order for the female die plate to obtain the aforesaid reverse orientation. In other cases, to obtain the reverse orientation, a table on which the coated steel plates are mounted may be inverted so that the stepping of the male and female die plates can be effected in the same sequential order. Differences in the sequential order of stepping and in the structure of the inverting table did not always produce the required high degree of accuracy of spacing between the stepped images due to the inherent inaccuracy of the mechanical mechanisms employed, as will be further discussed in the description of the preferred embodiment. Such inaccuracies between the spacing of the images resulted in inaccurate registry of the two die plates which in turn adversely affected the cutting action of the dies. Further, when it became necessary to make additional die plates, for example upon reorder at a later date, it was necessary to duplicate the time-consuming operation of stepping and repeating onto the photo resist of the die plates, with the possibility of introducing further inaccuracies relative to the die plates previously made.

In the present invention, the step and repeat operation may be performed in the same sequential order for both the male and female die plates without using an inversion table, wherein any inherent inaccuracies in the step and repeat machine are duplicated in the male and in the female die plates to enhance accuracy of registry of the die plates.

SUMMARY OF THE INVENTION A die for cutting sheet material comprises a pair of opposed coacting die members each having one of a coacting pair of cutting elements which partially overlap one another in the general plane of the material being cut. In producing such a die, a first image represents the cutting elements of one of said die members and a second image represents the cutting elements of the other of said die members. Each of the images representing the cutting elements includes an overlap section derived from a common image source to facilitate accuracy of registry of the two matched, coacting die plates derived from said images. The first image is stepped and repeated onto a first sheet of film so that the latter bears multiple, like images. The second image is stepped and repeated onto a second sheet of film through the base of the latter sheet of film so that the last said step and repeat operation is effected in the same sequential order as the first said step and repeat operation. The multiple images on said first and second sheets of film are optically transferred onto separate photosensitive surfaces leading toward production of a pair of matched, coacting die plates. Where desired, images representing coacting scoring elements are included on the die plates.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a part of a pair of opposed coacting die plates in register showing matched cutting and scoring elements thereon.

FIG. 2 is a plan view of a drawing used in making the die plates.

FIG. 3 is a magnified view of the portion of FIG. 2 included within the circle on the latter figure.

FIG. 4 is a schematic view indicating the various processing steps in making the die plates.

FIG. 5 is a cross-sectional view of a part of a pair of opposed coacting die plates showing matched, scoring elements and also showing, in phantom, the indicating media which represents said scoring elements.

FIG. 6 is a partial view of the indicating media representing the scoring elements shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The illustrated embodiment of the invention is par ticularly useful in making cutting and scoring die plates which are used in the formation of paperboard carton blanks. For convenience, a pair of die plates, which together comprise a die, will be herein designated as male and female die plates. A portion of a cutting and scoring die having male and female die plates 20 and 22 respectively is shown in FIG. 1. The male die plate 20 has a base portion 24 from which a cutting element 26 projects. The cutting element 26 is in the form of a projecting land which is formed integrally with the base portion 24. The male die plate 20 also has a male scoring element 28 projecting from and formed integrally with the base portion 24.

The female die plate 22, which cooperates with the male die plate 20 to effect a cutting and scoring of stock material disposed therebetween, has a pattern of cutting and scoring elements thereon which is related to the pattern of cutting and scoring elements on the male die plate 20. Specifically, the female die plate 22 has a base portion 32 from which a cutting element 30 projects, the latter being adapted to cooperate with the projecting cutting element 26 on the male die plate 20 to effect cutting of the stock material disposed between the die plates 20, 22. As will be further described, the cutting elements 26 and 30 overlap in the general plane of the stock material to be cut, such overlap being indicated by the letter O in FIG. 1. During the cutting operation, the cutting elements 26, 30 project into a portion of the stock material, but the cutting of the stock material is effected without any contact being made between the cutting elements 26 and 30.

The female die plate 22 also includes scoring elements 34, 36 which are integral with the base portion 32 and which are spaced apart so as to receive stock material forced therebetween by the male scoring element 28 on the male die plate 20. The die plates 20 and 22 may be flexible metal plates mounted on rotary cylinders by suitable clamps and, upon rotation, effect cutting and scoring of paperboard stock material advanced therebetween.

The pattern of the cutting and scoring elements on the die plates 20, 22 is such as to cut a box blank from the stock material and provide score lines thereon so as to permit folding of the cut-out box blank into a completed box or carton. The die plates 20, 22 are made to a size and configuration corresponding to the particular design of the box or carton blank desired. Thus, the partial showing in FIG. 1 is representative and illustrates the cutting and scoring elements of only one small section of the die plates. The die plates 20, 22 may cut a plurality of box blanks from the stock material at a given time and thus may have a plurality of like patterns formed thereon. The plurality of like patterns constitutes a plurality of die unit images, each die unit image corresponding to a single or unit box blank, cut from the stock material, along with a plurality of other, like unit blanks, by the die plates 20, 22. An example of an end use for die plates of this type and a method of operation thereof may be found in U.S. Pat. 3,142,233, issued July 28, 1964.

Among other things, the height and width of the male scoring element 28 and the width and depth of the groove between the female scoring elements 34, 36 influences the quality of the score which is formed in a paperboard sheet impression between the dies. The preferred dimensional relationship of the scoring elements is more particularly set forth in U.S. Pat. 3,341,329, issued Sept. 12, 1967.

The amount of horizontal overlap 0 (FIG. 1) of the coacting cutting elements 26 and 30 substantially affects the cutting operation. If there is too much overlap, the paperboard stock may not be cut satisfactorily. The amount of vertical gap G between the plates 20, 22 (i.e. the closest vertical distance between the working elements of the plates 20, 22 when the press is on impression) also affects the operation of the cutting elements 26, 30. The preferred dimensional relationship of the horizontal overlap O and the vertical gap G are more fully set forth in the aforementioned U.S. Pat. 3,341,329.

As previously indicated, the amount of overlap O is critical in effecting satisfactory cutting of the paperboard stock. It will be seen, as the description progresses, that provisions are made to provide accurate control of the relative position of the cutting element edges 38 and 40, which edges define the overlap 0, when the dies are on impression. Accordingly, the edges 38, 40 are sometimes hereinafter referred to as critical edges to distinguish them over the opposite edges 42, 44 of each cutting element 26, 30, respectively, which are not as critical because the overall width of the cutting elements 26, 30 may be of any convenient width consistent with the limitations of available space and the requirements of adequate strength to resist distortion and deformation. The portion of each cutting element 26, 30 not included as part of the overlap O is hereinafter sometimes referred to as the backup and is indicated by B in FIG. 1.

The die plates 20, 22 are formed by an etching process in which the metal plates are etched away except in the areas where the projecting working elements are to be formed. Prior to the etching of the plates 20, 22, any well-known photo-sensitive resist coating is placed on the surface thereof. The photosensitive resist coating is then exposed to light from a light source passing through a photographic negative which carries an image corresponding to the image or pattern of the cutting and scoring elements to be formed on the die plates 20, 22. Since the photographic negative is transparent only at the portions corresponding to the image thereon, a corresponding image is imposed on the resist coating. The area representing the image imposed on the resist coating receives light and becomes insoluble to the etchant which is subsequently applied. After the etching process, those areas of the plates beneath the hardened resist material become the working elements or lands which effect the cutting and scoring of the paperboard, stock material as heretofore described. Allowances are made for undercutting of the resist coating by the etching solution. It is known, for example, that for etching steel, an etching solution containing 20% nitric acid will undercut the resist coating approximately 0.010 inch per edge for an etching depth of 0.015 inch.

The photographic negatives from which the die plates 20, 22 are made are derived from a drawing of a carton blank, such drawing representing generally the composite working elements of the two die plates 20, 22, with allowance being made for undercutting of the resist coating by the etching solution as previously indicated.

Referring to FIG. 2, a sheet of material 48 bears a drawing 50 representing the composite working elements of the opposed die plates 20 and 22. Drawing 48 may be prepared on a suitable material such as paper or plastic film. Since, however, a high degree of precision is necessary in the dies produced, it is desirable that the material be one having high-dimensional stability. One example of an appropriate material is polyethylene terephthalate sheet. The lines of drawing 50 may be laid down accurately with an indicating medium such as ink or the like, but, preferably, they are laid down with color tapes of a pre-selected width, including allowances for undercutting, and color. More particularly, the outer peripheral lines (e.g. line 54) in FIG. 2 represent a composite of the cutting elements 26, 30 of the male and female die plates 20, 22 while other lines (e.g. line 52) represent a composite of the scoring elements 28, 34, 36 (see FIG. 1) of the male and female die plates 20, 22. As can be seen in the enlarged portion of drawing 50 in FIG. 3, an indicating medium 58 (e.g. red tape) represents the backup portion B of the cutting element 26 on the male die plate 20 and another indicating medium 56 (e.g. blue tape) represents the backup B of the cutting element 30 of the female die plate 22. Yet another indicating medium 60 (e.g. black tape) represents the areas at which the cutting elements 26, 30 of the two die plates overlap. Thus, in those areas of drawing 50 in which the black indicating medium 60 is sandwiched between the blue and red indicating media 56 and 58 respectively, the composite of the blue and black indicating media 56, 60 respectively, represents the cutting element 30 of the female die plate 22, and the composite of the red and black indicating media 58 and 60 respectively, represents the cutting element 26 of the male die plate 20. As can further be seen in the enlarged portion of drawing 50 in FIG. 3, indicating medium 56 (e.g., blue tape) also represents the female scoring elements 34, 36 of the female die plate 22, and indicating medium 58 (e.g. red tape) also represents the male scoring element 28 of the opposed male die plate 20.

The indicating media 56, 58, 60 are selected such that media 56 and 58 are separable from each other by the use of color filters or the use of sets of different colored lights to illuminate sheet 48 at the time when images therefrom are imposed on a color-sensitive photographic surface, or by the use of photographic films sensitized to some wave lengths but insensitive to others. Indicating medium 60 is such that the optical-photographic techniques used to selectively separate out media 56 and 58 do not separate out medium 60.

In the preferred mode of carrying out the method, media 56 and 58 are of complementary colors which easily can be separated from each other by the use of color filters. Although these colors are indicated in the drawings as being blue and red, many other combmations of complementary colors will immediately be ObVlous to those skilled in the art, such as red and green, yellow and blue, and orange and purple. The media need not be colors, but one of the media could instead be a composition which fluoresces under given lighting conditions, whereas the other medium might be a particular shade of gray, which could easily be separated by lighting techniques from the fiuorescing composition.

Medium 60 is shown in FIG. 3 to be black. However, it should be obvious that many other colors would also be suitable, particularly, in this instance, purple, which is a combination of the blue and red in FIG. 3. It will be understood from the following description that in some cases the third medium will be unnecessary since no overlapping of the working surfaces on the drawing 48 may be needed, for example, when only scoring, and not cutting, is to be performed by the dies. As previously indicated, allowances are made throughout for undercutting of the resist coating by the etching solution.

As previously indicated, allowances are made for undercutting and the aforesaid drawing 50 is multiplied by a sizing factor (e.g. a sizing factor of five). A camera is set for size reduction by a factor of five. Two photographic negatives obtained by a camera set for size reduction by the aforesaid sizing factor are made of drawing 50. One photographic negative 70 (FIG. 4) bears an imposed composite image of the area indicated by indicating media 58 (red tape) and 60 (black tape). The area indicated by medium 56 (blue tape) is not imposed on photographic negative 70 because it is excluded by means of optical-photographic techniques, for example, by using one or more filters which absorb the color (blue) of medium 56. A second photographic negative 72 bears an imposed composite image of the area indicated by media 56 (blue tape) and 60 (black tape) and is obtained by photographing the drawing 50 and eliminating any image of medium 58 (red tape) by optical-photographic techniques, for example, by using one or more filters which absorb the color (red) of medium 58.

From the above description it will be seen that photographic negative 70 bears an image representing the male scoring element 28 and the cutting element 26 of the male die plate 20 (said latter cutting element 26 being made up of overlap 0 plus backup B). Photographic negative 72 bears an image representing the female scoring elements 34, 36 and the cutting element 30 of the female die plate 22 (said latter cutting element 30 being made up of overlap 0 plus backup B). The processing of the two negatives 70, 72, each negative having a single unit image, either a male die unit image or a female die unit image, to obtain the male and female die plates 20, 22 each plate having a plurality of like, unit images, either a plurality of male die unit images or a plurality of female die unit images, is shown schematically in the flow sheet of FIG. 4.

It will be apparent that making drawing 50 on an enlarged scale and obtaining a size reduction photographically as the two photographic negatives 70, 72 are made increases the accuracy of the positioning of the working surfaces of the die plates to be produced. Thus, for example, if the accuracy attainable in the method of making drawing 50 is :0.005 inch, and the size of the images on negatives 70, 72 is reduced by a factor of 5, the maximum error in the photographically imposed image on negative 70, 72 will be only $0.001 inch.

Referring to the flow sheet in FIG. 4, each of the photographic negatives 70, 72 is processed in a manner to produce other negatives from which the die plates 20, 22 are ultimately made. In the first step of their processing, photographic positives 7-4 and 7.6 are made from negatives 7t) and 72 respectively. The positive 76 is made by contacting through the base of negative 72 according to known procedures. By contacting through the base of the negative, it is meant that the emulsion of negative 72 and the emulsion of the raw film on which the positive 76 is made both face upwardly so that the image on the positive 76 has the same orientation as the image on the negative 72 from which it is derived. This latter fact will be apparent by the fact that the reference indicia R in FIG. 4 on the negative 72 and positive 76 face in the same direction.

In making the positive 76 a point source light is disposed a relatively long distance from the negative 72 to minimize the light spread as the light rays from the point source light penetrate the space between the emulsion, said space being occupied by the backing of the negative 72. Accordingly, there is a minimum line growth or parallactic displacement of the image as it is transferred from the photographic negative 72 to positive 76. After the positive 76 is made, negative 72 is preserved.

Following the processing path in FIG. 4, photographic negative 80 is made from positive 76. The positive 76 is contacted, according to known procedures, with the emul sions face-toface so that the image on the negative 80 is a lateral reversal of the image on the positive 76 from which it is derived. Lateral reversal of the image will be apparent by comparing the reference indicia R in FIG. 4 on the respective positive 76 and negative 80.

Returning to the negative 70 and positive 74, the latter is made from the former using an arrangement where the emulsion of negative 70 faces downwardly and the emul sion of the raw film from which the positive 74 is made faces upwardly. A clear spacer, e.g. a transparent plastic sheet (not shown), is disposed between the downwardly and upwardly facing emulsions so that the latter are spaced apart an amount equal to the thickness of the spacer. The desirability of using a spacer at this point of the processing will become apparent as the description proceeds. It will be seen that the aforedescribed arrange ment results in a lateral reversal of the image on positive 74 with respect to the image on negative 70 as indicated by comparing the reference indicia R in FlG. 4 on negative 70 and positive 74.

In making the positive 74, a point source light is disposed a relatively long distance above the respective negative 70, to minimize the light spread as the light rays from the point source light penetrate the space between the emulsions, said space being occupied by the previously described spacer (not shown). Accordingly, there is a minimum line growth or parallactic displace ment of the image as it is transferred from the photographic negative 70 to the positive 74. After the positive 74 is made, the negative 70 is preserved.

Following the processing path in FIG. 4, photographic negative 78 is made from positive 74. The positive 74 is contacted, according to known procedures, with the emulsions face-to-face so that the image on the negative 78 is a lateral reversal of the image on the positive 74 from which it is derived. Lateral reversal of the images will be apparent by comparing the reference indicia R in FIG. 4 on the positive 74 and negative 78.

From the above, it will be seen that the images on the positives 74 and 76 are reversed with respect to one another. Further, each positive 74 and 76 is derived from a negative 70, 72 respectively, each having their emulsions spaced from one another, in one case by a clear, plastic spacer and, in the other case, by the base of the film. In this regard, it is pointed out that the plastic spacer has a thickness equal to that of the base of the film so that any light spread or parallactic displacement will be the same in each case. However, it should be pointed out that the point source light minimizes the light spread as the light rays from the point source light penetrate the space occupied by the spacer (not shown) between the negative 70 and positive 74 in one case, and the space occupied by the base of negative 72 in the other case. Ac-

cordingly, the light spread is minimal and any resulting line growth of the images as they are transferred from photographic negatives 70, 72 to photographic positives 74, 76 respectively are substantially equal.

Since photographic negatives 78 and 80 are derived from line drawing 50 which represents a single carbon blank, and it is desirable to produce a die that will cut and score a number of carton blanks in a single processing operation, the negatives 78, '80 are photomechanically stepped and repeated to produce larger photographic negatives 82, 84 respectively, each having a plurality of like images arranged adjacent to one another. The photo graphic negatives 82, 84 are made on duplicating or reversal film of the type wherein the character (positive or negative) of the image to be imposed on the reversal film is the same as the character of the image imposed on said reversal film. More specifically, negatives 78 and 80 are stepped and repeated onto sheets of raw, negative reversal film to produce directly, negatives 82 and 84 respectively, without intervening operations of going from negative to positive and back again to negative. An example of a commercially available duplicating or reversal film suitable for this purpose is Kodalith duplicating film having an Estar base manufactured by Kodak.

As the negative 78 is stepped, it is contacted through the base of the negative 78 according to known procedures. In contacting through the base of negative 78, the emulsion of the negative 78 and the emulsion of the raw reversal film on which the negative 82 is formed face upwardly so that the image on the negative 82 has the same orientation as the image on the negative 78. A point source light is disposed a relatively long distance above the negative 78 to minimize the light spread as the light rays from the point source light penetrate the space between the emulsions, said space being occupied by the backing of the negative 78.

As the negative is stepped, it is contacted through the base of the raw reversal film on which the negative 84 formed. In contacting in this manner, the emulsion of negative 80 and the emulsion of the raw reversal film on which the negative 84 is formed face downwardly. A point source light above the negative 80 minimizes the light spread as the light rays from the point source light penetrate the space between the emulsions, said space being occupied by the backing of negative 84.

It will be seen that each negative 82, 84 is derived from a negative 78, 80 respectively, each having their emulsions spaced from one another, in one case by the base of the negative (i.e. negative 78) which is to be stepped, and, in the other case, by the base of the raw reversal film (i.e. negative 84) on which the negative (i.e. negative 80) is to be stepped. The thickness of the photographic film used is substantially equal so that any light spread or parallactic displacement will be substantially the same in each case. Here again, the two negatives 82, 84 are obtained utilizing a point source light so that the light spread is minimized.

In order that the spacing between the plurality of images in photographic negatives 82 and 84 correspond as accurately as possible to one another to enhance registry of the die plates ultimately derived therefrom, the negatives 82, 84 are obtained by stepping the negatives 78, 80 respectively, on the same stepping machine and in the same sequential order.

Viewing negative 82 in FIG. 4, it will be seen that the stepping is effected from left to right, e.g. from R to R This is accomplished with the emulsions of negatives 78 and 82 both facing upwardly as previously described.

The stepping of negative 80 to produce negatives 84 is also effected in the same sequential order (i.e. from left to right) from R to R The fact that R is shown to the right of R in negative 84 in FIG. 4 is not an inconsistency as will be explained. First of all, in order to maintain consistency in the drawing (FIG. 4), all the negatives (i.e. 70, 72, 78, 80, 82, 84) and positives (i.e. 74, 76) are depicted with their emulsions facing upwardly. It will be recalled that when negative 80 is stepped onto negative 84, the emulsion of both negatives 80, 84 are arranged to face downwardly. Accordingly, when negative 80 is stepped onto negative 84, both such negatives are inverted, that is, they are flipped over to dispose their emulsion from the upward facing dispositions shown in FIG. 4 to a downward facing disposition (not shown). The image on negatives 80, 84 (when the latter are flipped over as aforesaid) as viewed from above, appear as lateral reversals of that shown in FIG. 4. Expressed otherwise, when negatives 80, 84 are inverted or flipped over, the indicia R in both negatives 80, 84 appear normally as in print and in negative 84, R is located to the left of R Accordingly, with each negative 80, 84 arranged in the stepping machine with their emulsions facing downwardly, the sequential order of stepping will be from left to right (from R to R Of course, after the stepping operation to obtain negative 84 is completed, said negative 84 when removed from the stepping machine is inverted or flipped over to dispose its emulsion upwardly facing and it appears as shown in FIG. 4.

From the above description it will be seen that both multi-image negatives 82 and 84 are obtained by stepping each single image negative 78 and 80 respectively, from left to right, or more generically, by stepping each single image negative 78 and 80 in the same sequential order. By following this procedure, any inaccuracy in the stepping machine is duplicated in both negatives 82, 84 as to spacing of the images thereon. For example, the stepping machine may utilize a mechanical mechanism (e.g. a rotatable lead screw effecting longitudinal displacement of a block element which is in threaded engagement with the lead screw) to advance or step a carrier (not shown) on which the negative 78 is mounted, from one position to an adjacent position. The same procedure on the same machine is followed in stepping negative 80 between corresponding positions. The same sequential stepping order is followed for stepping the images in a longitudinal and transverse direction in obtaining the negatives 82, 84.

In this regard, it is noted that a high degree of accuracy is desirable in obtaining registry of image spacing on the two negatives 82, 84 because, as will be described hereinafter, these negatives are used to make the die plates. By following the same sequential stepping order in making the negatives 82, 84 the effect of the inherent inaccuracy in the mechanical mechanism of the stepping machine is minimized. In contrast, it will be appreciated that the accuracy between a lead screw and a meshing threaded block is such that the lead screw in rotating a prescribed number of turns will advance the block in one direction a predetermined distance and that this can be repeated or duplicated with a high degree of accuracy along the identical portion of the lead screw in advancing the block in the same direction. However, the same predetermined distance will not be obtained with the same high degree of accuracy by rotating the lead screw the same prescribed number of turns in an opposite direction because different faces or sides of the lead screw and threaded block are involved.

As will be described, negative 82 is utilized to impose its image on the photoresist of the male die plate20 to ultimately produce the working elements on said male die plate. Similarly, negative 84 is utilized to impose its image on the photoresist of the female die plate 22 to ultimately produce the working elements of said female die plate 22.

The negative 82, with its emulsion down, is placed on the photoresist of male die plate 20 with the emulsion in direct contact with the photoresist and, by exposure to light, the images on negative 82 are imposed onto the photoresist. Thereafter, negative 82 is removed from the photoresist.

The area on the photoresist coating defining the images becomes insoluble to the etching solution. The exposed metal die plate 20 is developed and fixed in a conventional manner, the unexposed photoresist coating being washed away with water. The resulting die plate 20, bearing a protective photoresist coating only in those areas corresponding to the male scoring element 28 and the male cutting element 26, allowance having been made for undercutting, is etched in a suitable etchant bath to a suitable depth, and finished die plate 20 bears said cutting and scoring elements 26 and 28 respectively as raised lands.

The image on the photoresist of female die plate 22 is derived from negative 84 using the same basic procedure just described. More specifically, the negative 84 with its emulsion down, is placed on the photoresist of female die plate 22 with the emulsion in direct contact with the photoresist and, by exposure to light, the images on negative 84 are imposed onto the photoresist. Thereafter negative 84 is removed from the photoresist.

The area on the photoresist coating defining the images hardens and becomes insoluble in the etching solution. The exposed metal die plate 22 is then processed in the manner previously described for the male die plate 20, whereby the finished die plate 22 bears the female scoring elements 34, 36 and the cutting element 30 as raised lands.

The die plates 20, 22 may be made of any of a variety of etchable metals such as magnesium, copper, steel, bronze and the like, the choice of the particular metal to be utilized in a given case being determined by the relative importance of various factors such as durability, rapidity and ease of etching, flexibility, economy and other factors. The etching medium used will depend on the particular metal which is to be etched, satisfactory etchants for each of the metals listed as well as other etchable metals being well-known in the art. In general, magnesium is most often etched in a bath composition based primarily on nitric acid while copper, steel, and bronze are customarily etched with ferric chloride etchant compositions, although ammonium persulfate and other oxidizing etchants may also be used. Similarly, the die plates 20, 22 may be of a photopolymerizable plastic composition, such as photosensitized nylon or a photopolymerizable composition of a divinyl ester of a polyethylene glycol or the like.

From the above description, it will be observed that the image imposed on the photoresist of male die plate 20 is a lateral reversal of the image imposed on the photoresist of female die plate 22. Accordingly, when one of the die plates is inverted in order to mate with the other die plate in the manner shown in FIG. 1, the cutting and scoring elements will be properly oriented to provide the cutting and scoring action previously described.

It will be recalled that indicating media on the drawing 50 includes allowance for undercutting of the photoresist coating by the etching solution. In some cases, in allowing for undercutting, the indicating media representing the male and female scoring elements may overlap. To illustrate this, a representation of the indicating media which would be required for the scoring elements, including allowance for undercutting, are shown in. phantom in FIG. 5 adjacent to scoring elements which said indicating media represent. The features in FIG. 5 are similar in many respects to those heretofore shown and described. Accordingly, like parts are identified by similar numerals with the addition of the sufiix x, thereby obviating the necessity of extended and repetitive discussion.

It will be seen in FIG. 5 that indicating medium 56 representing the female scoring elements 34x, 36x and indicating medium 58 representing the male scoring element 28x overlap. The overlapping portions are represented by the same indicating medium 60 (e.g., black) which is not separated out by the optical-photographic techniques used to selectively separate out media '56 and 58. The indicating media representing the scoring elements 28x, 34x, 36x would appear on drawing 50 as shown in FIG. 6. The image on negative 72 corresponding to the female scoring elements 36x, 34x, respectively are made up of a composite of indicating media 56 and 60. The image on negative 70 corresponding to the male scoring element 28x is made up of a composite of indicating media 58 and 60. Accordingly, the desired images of the male and female scoring elements are imposed on negatives 70 and 72 respectively and carried through the processing of the film until imposed on the photoresist of the male and female die plates.

An alternate method of making the die plates consists of stepping and repeating the photographic negatives 70 and 72 directly onto separate sheets of reversal film to provide multiple images on said reversal film and thereafter proceeding, as in the main embodiment, to transfer the multiple images directly onto the photoresist surfaces. In this alternate arrangement, negative 70 would be stepped, with its emulsion down, onto the reversal film with the latter having its emulsion up, but with a clear spacer between the emulsions. This will result in a lateral reversal of the image imposed on the reversal film. Negative 72 would he stepped and repeated as is negative in the main embodiment, that is, through the base of the reversal film on which the negative 72 is stepped. In this alternate arrangement, the same sequential stepping order would be followed in each stepping operation.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the steps of the method described and their order of accomplishment without departing from the spirit and scope of the invention or sacrificing any of its material advantages, the method hereinbefore described being merely a preferred embodiment thereof.

We claim:

1. In a method for producing a cutting and scoring die for working a sheet material along a preselected pattern of cut lines and score lines to provide a plurality of cut and scored, sheet unit blanks, said die comprising a pair of opposed, coacting die members, each member being all of one homogeneous piece, which method includes the step of forming a first negative and a second negative, each negative having a single unit image thereon, one negative having a female die unit image and the other negative having a male die unit image, each unit image corresponding to one of the unit blanks, the improvement which comprises the steps of:

stepping and repeating in a precise, sequential order of photomechanical processing said first negative on to a first sheet of film so that a sequential plurality of unit images are produced on said first sheet of film;

stepping and repeating in the same, precise sequential order of photomechanical processing said second negative on to a second sheet of film, having a transparent base, so that a sequential plurality of unit images are produced on said second sheet of film having a laterally reverse orientation from the orien tation of each unit image of the sequential plurality of unit images produced on said first sheet of film; said stepping and repeating of said second negative including the contacting of said second negative through the base of said second sheet of film so that the sequential order of unit images on said second sheet of film is laterally reversed from the sequential order of unit images on said first sheet of film; optically transferring the plurality of unit images on said first and second sheets of film on to separate,

photosensitive surfaces; and

removing by chemical means material from said photosensitive surfaces except in the regions bearing said multiple, like unit images to produce a pair of matched, opposed, coacting die plates.

2. A method according to claim 1 wherein said first negative is exposed through the base thereof during the stepping and repeating thereof on to said first sheet of film.

3. A method according to claim 1 wherein the photosensitive emulsions on said first negative and on said first sheet of film face in the same vertical direction during their stepping and repeating step; the photosensitive emulsion on said first and second negatives facing in opposite vertical directions during their respective stepping and repeating steps and having unit images with laterally reversed orientation.

References Cited UNITED STATES PATENTS 1,761,863 6/1930 Bassist 96-Regist. Dig. 2,499,100 2/1950 Kessler 96Regist. Dig. 3,005,364 10/1961 Broderick 9630 3,341,329 9/1967 Blake 96-36 MURRAY KATZ, Primary Examiner US. Cl. X.R. 

